Leveraging primary effluent- and glycerol-driven partial denitrification-anammox within a pilot-scale tertiary step-feed moving bed biofilm reactor treating high-rate activated sludge systems effluent.

This study investigated the possibility of utilizing primary effluent (PE) carbon as an internal carbon source to drive tertiary partial denitrification-anammox (PdNA) for treating high-rate activated sludge (HRAS) system effluent, so as to offset the consumption of external carbon such as glycerol. This pilot study was conducted in a tertiary step-feed moving bed biofilm reactor (MBBR) over 478 days, using full-scale HRAS secondary effluent as the influent. Unlike most PdNA applications that rely on the expensive supplemental carbon like methanol or glycerol, this study is the first to demonstrate that PE carbon can be utilized as a naturally available carbon source within wastewater to drive PdNA. By taking advantage of this free internal carbon source to driven PdNA, 63% to 74% savings in PE carbon consumption and ∼36% offset in glycerol consumption were achieved. Additionally, glycerol-driven PdNA further reduced both supplemental carbon and aeration energy demands by 70% and 18%. Mechanistic insights from in-situ and ex-situ batch tests revealed that the PE-driven PdNA was facilitated by an anammox-driven nitrite sink, a novel observation that allowed stable PdNA performance without nitrite accumulation. Furthermore, batch tests indicated that endogenous respiration could support PdNA. These findings highlight the potential of applying PE-driven PdNA in full-scale facilities, ushering in a new era of mainstream anammox applications in wastewater treatment, as PdNA is no longer reliant on costly external carbon addition.